Multi-element resonator

ABSTRACT

A resonant tank includes a first capacitor formed on a semiconductor substrate, a first inductor formed on the semiconductor substrate, a second capacitor formed on the semiconductor substrate, and a second inductor formed on the semiconductor substrate. The first capacitor, the first inductor, the second capacitor, and the second inductor are connected in a ring configuration, with each capacitor connected between a pair of the inductors and with each inductor connected between a pair of the capacitors. An amplifier circuit is coupled to the resonant tank and configured to amplify a signal in the resonant tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/029,905(now U.S. Pat. No. 10,924,059), filed on Jul. 9, 2018, thedisclosures of which are hereby incorporated by reference in theirentireties.

FIELD

The disclosure generally relates to electrical circuits includingintegrated circuits used in communications.

BACKGROUND

Electronic circuits, including electronic circuits formed as integratedcircuits (ICs) on semiconductor substrates, are used in a variety ofapplications including in communication systems. For example, atransmitter circuit may be formed of one or more integrated circuitsformed on one or more silicon substrates and a receiver circuit may beformed of one or more integrated circuits formed on one or more siliconsubstrates. In general, there is a trend in integrated circuittechnology towards smaller feature size in order to make circuitssmaller and reduce cost. Smaller feature sizes may affect circuits inmany ways and not all circuits scale identically. As feature sizes getsmaller, devices may have lower breakdown voltages, which may beovercome by designing for lower voltages to ensure that breakdownvoltages are not exceeded. Lower voltages may affect IC characteristicsincluding IC characteristics of transmitter and receiver circuits formedas or of ICs.

BRIEF SUMMARY

According to one aspect of the present disclosure, there is provided anoscillator circuit comprising: a resonant tank including a firstcapacitor formed on a semiconductor substrate, a first inductor formedon the semiconductor substrate, a second capacitor formed on thesemiconductor substrate, and a second inductor formed on thesemiconductor substrate, the first capacitor, the first inductor, thesecond capacitor, and the second inductor connected in a ringconfiguration with each capacitor connected between a pair of theinductors and each inductor connected between a pair of the capacitors;and an amplifier circuit coupled to the resonant tank and configured toamplify a signal in the resonant tank.

Optionally, in any of the preceding aspects, each of the first inductorand the second inductor is formed by one or more respective portions ofmetal deposited on the semiconductor substrate.

Optionally, in any of the preceding aspects, the first inductor andsecond inductor are tapped inductors each having at least one tappedinput terminal at an intermediate location between inductor ends.

Optionally, in any of the preceding aspects, the amplifier circuitincludes a first inverter connected to a said tapped input terminal ofthe first inductor and a second inverter connected to a said tappedinput terminal of the second inductor.

Optionally, in any of the preceding aspects, the amplifier circuitincludes a first pair of inverters connected across the first inductorand a second pair of inverters connected across the second inductor.

Optionally, in any of the preceding aspects, the first capacitor is avariable capacitor with a capacitance that is variable over apredetermined range to control a resonant frequency of the oscillatorcircuit.

Optionally, in any of the preceding aspects, the first capacitorcomprises at least a first capacitive element and a second capacitiveelement with one or more switches to modify a capacitance of the firstcapacitor by discrete amounts according to connection of the firstcapacitive element and the second capacitive element.

Optionally, in any of the preceding aspects, the first capacitorincludes one or more variable capacitive elements each with a respectivecapacitance that is variable over a continuous range according to anapplied voltage.

Optionally, in any of the preceding aspects, the oscillator circuitforms a Voltage Controlled Oscillator (VCO) in a Phase Locked Loop (PLL)circuit that further includes a feedback loop, a phase detector, and afilter.

Optionally, in any of the preceding aspects, the Phase Locked Loop (PLL)circuit is configured to provide an oscillator signal in a transmitteror receiver in user equipment in a communications system.

Optionally, in any of the preceding aspects, the oscillator circuit alsoincludes a third capacitor formed on the semiconductor substrate, athird inductor formed on the semiconductor substrate, a fourth capacitorformed on the semiconductor substrate, and a fourth inductor formed onthe semiconductor substrate. The third capacitor, the third inductor,the fourth capacitor, and the fourth inductor are connected with thefirst capacitor, the first inductor, the second capacitor, and thesecond inductor in the ring configuration with each capacitor connectedbetween a pair of the inductors and each inductor connected between apair of the capacitors.

According to one other aspect of the present disclosure, there isprovided a method of generating an oscillator signal comprising:receiving an electrical signal from a resonant tank, the resonant tankincluding a first capacitor formed on a semiconductor substrate, a firstinductor formed on the semiconductor substrate, a second capacitorformed on the semiconductor substrate, and a second inductor formed onthe semiconductor substrate. The first capacitor, the first inductor,the second capacitor, and the second inductor are connected in series ina ring configuration with each capacitor connected in series betweeninductors and each inductor connected in series between capacitors. Themethod also includes amplifying the electrical signal from the resonanttank and providing an amplified electrical signal back to the resonanttank to generate the oscillator signal at a resonant frequency of theresonant tank.

Optionally, in any of the preceding aspects, amplifying the electricalsignal is performed using one or more pairs of inverters.

Optionally, in any of the preceding aspects, the first inductor and thesecond inductor are tapped inductors each having at least one tappedterminal at an intermediate location between inductor ends, andproviding the amplified electrical signal back to the resonant tankincludes providing inverted amplified signals at tapped terminals of thefirst and second inductors.

Optionally, in any of the preceding aspects, the method further includescontrolling a capacitance of at least the first capacitor to control theresonant frequency and thereby control frequency of the oscillatorsignal.

Optionally, in any of the preceding aspects, the method further includesobtaining a carrier signal in a transceiver of in a communicationssystem from the oscillator signal.

Optionally, in any of the preceding aspects, obtaining the carriersignal in the transceiver includes performing phase comparison andfiltering in a Phase Locked Loop (PLL).

According to still one other aspect of the present disclosure, there isprovided a Voltage Controlled Oscillator (VCO), comprising: a resonanttank; a first inverter; and a second inverter. The resonant tankincludes: a first capacitor formed on a semiconductor substrate; asecond capacitor formed on the semiconductor substrate; a first inductorformed on the semiconductor substrate, the first inductor having a firsttapped terminal, the first inductor connected between a first terminalof the first capacitor and a first terminal of the second capacitor; asecond inductor formed on the semiconductor substrate, the secondinductor having a second tapped terminal, the second inductor connectedbetween a second terminal of the first capacitor and a second terminalof the second capacitor such that the first capacitor, the firstinductor, the second capacitor, and the second inductor form a ring. Thefirst inverter has an input connected to the first terminal of the firstcapacitor and an output connected to the first tapped terminal. Thesecond inverter has an input connected to the second terminal of thefirst capacitor and an output connected to the second tapped terminal.

Optionally, in any of the preceding aspects, at least one of the firstcapacitor and the second capacitor is a variable capacitor having avariable capacitance controlled to select a resonant frequency of theresonant tank.

Optionally, in any of the preceding aspects, the VCO is connected to aphase detector, a filter, and a feedback loop in a Phase Locked Loop(PLL) arrangement to provide an oscillator signal of a transceiver.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. The claimed subject matter is not limited to implementationsthat solve any or all disadvantages noted in the Background.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are illustrated by way of example andare not limited by the accompanying figures (FIGS.) for which likereferences indicate elements.

FIGURE (FIG. 1 illustrates an exemplary wireless network forcommunicating data.

FIG. 2 illustrates exemplary details of an instance of user equipment(UE) introduced in FIG. 1.

FIG. 3 illustrates exemplary details of an instance of a base station(BS) introduced in FIG. 1.

FIG. 4 illustrates exemplary details of a receiver included in a UE or aBS shown in FIGS. 2 and 3.

FIG. 5 illustrates exemplary details of a transmitter included in a UEor a BS shown in FIGS. 2 and 3.

FIG. 6 illustrates an example of a PLL included in in a UE or a BS shownin FIGS. 2 and 3 as illustrated in FIGS. 4 and 5.

FIGS. 7A-F illustrate examples of VCOs included in the PLL of FIG. 6.

FIGS. 8A-C illustrate an example of an LC tank that may be included inthe VCOs of FIGS. 7A-B.

FIGS. 9A-D illustrate another example of an LC tank that may be includedin the VCOs of FIGS. 7A-B.

FIGS. 10A-D illustrate implementations of the LC tank of FIGS. 9A-D in aVCO such as the VCOs of FIGS. 7A-B.

FIGS. 11A-C illustrate implementations of the VCOs of FIGS. 7A-B usingtapped inductors.

FIG. 12 illustrates an implementation of an LC tank with more than twocapacitors and more than two inductors in a ring configuration that maybe used in the VCOs of FIGS. 7A-B.

FIG. 13 illustrates a high level flow diagram that is used to summarizevarious methods of operating a resonant tank, such as the LC tanks ofFIGS. 9A-12.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to thefigures, which in general relate to Voltage Controlled Oscillator (VCO)circuits that include an inductor-capacitor (LC) resonant tank.

A resonant tank in an oscillator circuit such as a VCO may be formed bya capacitor and an inductor. In general, as device dimensions shrink,breakdown voltages become smaller and lower voltages may be used inorder to avoid breakdown. However, lower voltages may result in lowersignal to noise ratio (SNR) and lower Quality Factor (Q factor) in somecircuits, including circuits used in user equipment in a communicationssystem. In order to maintain SNR at a given frequency while reducingvoltage, capacitor size may be increased while inductor size is reduced.However, this approach is not always feasible. Devices with m is-matchedsizes may be difficult or impossible to physically connect at somescale.

A resonant tank formed by a multi-element ring of capacitors andinductors may allow the use of lower voltages, while maintaining anacceptable SNR, and while maintaining relative sizes of capacitors andinductors within an acceptable range. For example, two capacitors andtwo inductors may be coupled together in an alternating ringconfiguration. For the same voltage as a single-capacitor,single-inductor resonant tank, such a two-capacitor, two-inductorresonant tank may store approximately double the energy and may providea signal with approximately double the SNR. Using half the voltage asused in a single-capacitor, single-inductor resonant tank, such atwo-capacitor, two-inductor resonant tank may store approximately thesame amount of energy and may provide a signal with approximately thesame SNR thus facilitating acceptable SNR as devices shrink and voltagesare reduced.

It is understood that the present embodiments of the disclosure may beimplemented in many different forms and that claims scopes should not beconstrued as being limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete and will fully convey the inventive embodiment concepts tothose skilled in the art. Indeed, the disclosure is intended to coveralternatives, modifications and equivalents of these embodiments, whichare included within the scope and spirit of the disclosure as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present embodiments of the disclosure, numerous specific detailsare set forth in order to provide a thorough understanding. However, itwill be clear to those of ordinary skill in the art that the presentembodiments of the disclosure may be practiced without such specificdetails.

FIG. 1 illustrates a wireless network for communicating data. Thecommunication system 100 includes, for example, user equipment110A-110C, radio access networks (RANs) 120A-120B, a core network 130, apublic switched telephone network (PSTN) 140, the Internet 150, andother networks 160. Additional or alternative networks include privateand public data-packet networks including corporate intranets. Whilecertain numbers of these components or elements are shown in the figure,any number of these components or elements may be included in the system100.

In one embodiment, the wireless network may be a fifth generation (5G)network including at least one 5G base station which employs orthogonalfrequency-division multiplexing (OFDM) and/or non-OFDM and atransmission time interval (TTI) shorter than 1 ms (e.g. 100 or 200microseconds), to communicate with the communication devices. Ingeneral, a base station may also be used to refer any of the eNB and the5G BS (gNB). In addition, the network may further include a networkserver for processing information received from the communicationdevices via the at least one eNB or gNB.

System 100 enables multiple wireless users to transmit and receive dataand other content. The system 100 may implement one or more channelaccess methods, such as but not limited to code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal FDMA (OFDMA), or single-carrier FDMA(SC-FDMA).

The user equipment (UE) 110A-110C are configured to operate and/orcommunicate in the system 100. For example, the user equipment 110A-110Care configured to transmit and/or receive wireless signals or wiredsignals. Each user equipment 110A-110C represents any suitable end userdevice and may include such devices (or may be referred to) as a userequipment/device, wireless transmit/receive unit (UE), mobile station,fixed or mobile subscriber unit, pager, cellular telephone, personaldigital assistant (PDA), smartphone, laptop, computer, touchpad,wireless sensor, wearable devices or consumer electronics device.

In the depicted embodiment, the RANs 120A-120B include one or more basestations 170A, 170B (collectively, base stations 170), respectively.Each of the base stations 170 is configured to wirelessly interface withone or more of the UEs 110A, 110B, 110C to enable access to the corenetwork 130, the PSTN 140, the Internet 150, and/or the other networks160. For example, the base stations (BSs) 170 may include one or more ofseveral well-known devices, such as a base transceiver station (BTS), aNode-B (NodeB), an evolved NodeB (eNB), a next (fifth) generation (5G)NodeB (gNB), a Home NodeB, a Home eNodeB, a site controller, an accesspoint (AP), or a wireless router, or a server, router, switch, or otherprocessing entity with a wired or wireless network.

In one embodiment, the base station 170A forms part of the RAN 120A,which may include other base stations, elements, and/or devices.Similarly, the base station 170B forms part of the RAN 120B, which mayinclude other base stations, elements, and/or devices. Each of the basestations 170 operates to transmit and/or receive wireless signals withina particular geographic region or area, sometimes referred to as a“cell.” In some embodiments, multiple-input multiple-output (MIMO)technology may be employed having multiple transceivers for each cell.

The base stations 170 communicate with one or more of the user equipment110A-110C over one or more air interfaces (not shown) using wirelesscommunication links. The air interfaces may utilize any suitable radioaccess technology.

It is contemplated that the system 100 may use multiple channel accessfunctionality, including for example schemes in which the base stations170 and user equipment 110A-110C are configured to implement the LongTerm Evolution wireless communication standard (LTE), LTE Advanced(LTE-A), and/or LTE Multimedia Broadcast Multicast Service (MBMS). Inother embodiments, the base stations 170 and user equipment 110A-110Care configured to implement UMTS, HSPA, or HSPA+ standards andprotocols. Of course, other multiple access schemes and wirelessprotocols may be utilized.

The RANs 120A-120B are in communication with the core network 130 toprovide the user equipment 110A-110C with voice, data, application,Voice over Internet Protocol (VoIP), or other services. As appreciated,the RANs 120A-120B and/or the core network 130 may be in direct orindirect communication with one or more other RANs (not shown). The corenetwork 130 may also serve as a gateway access for other networks (suchas PSTN 140, Internet 150, and other networks 160). In addition, some orall of the user equipment 110A-110C may include functionality forcommunicating with different wireless networks over different wirelesslinks using different wireless technologies and/or protocols.

The RANs 120A-120B may also include millimeter and/or microwave accesspoints (APs). The APs may be part of the base stations 170 or may belocated remote from the base stations 170. The APs may include, but arenot limited to, a connection point (an mmW CP) or a base station 170capable of mmW communication (e.g., a mmW base station). The mmW APs maytransmit and receive signals in a frequency range, for example, from 24GHz to 100 GHz, but are not required to operate throughout this range.As used herein, the term base station is used to refer to a base stationand/or a wireless access point.

Although FIG. 1 illustrates one example of a communication system,various changes may be made to FIG. 1. For example, the communicationsystem 100 could include any number of user equipment, base stations,networks, or other components in any suitable configuration. It is alsoappreciated that the term user equipment may refer to any type ofwireless device communicating with a radio network node in a cellular ormobile communication system. Non-limiting examples of user equipment area target device, device-to-device (D2D) user equipment, machine typeuser equipment or user equipment capable of machine-to-machine (M2M)communication, laptops, PDA, iPad, Tablet, mobile terminals, smartphones, laptop embedded equipped (LEE), laptop mounted equipment (LME)and USB dongles.

FIG. 2 illustrates example details of an UE 110 that may implement themethods and teachings according to this disclosure. The UE 110 may forexample be a mobile telephone, but may be other devices in furtherexamples such as a desktop computer, laptop computer, tablet, hand-heldcomputing device, automobile computing device and/or other computingdevices. As shown in the figure, the exemplary UE 110 is shown asincluding at least one transmitter 202, at least one receiver 204,memory 206, at least one processor 208, and at least one input/outputdevice 212. The processor 208 can implement various processingoperations of the UE 110. For example, the processor 208 can performsignal coding, data processing, power control, input/output processing,or any other functionality enabling the UE 110 to operate in the system100 (FIG. 1). The processor 208 may include any suitable processing orcomputing device configured to perform one or more operations. Forexample, the processor 208 may include a microprocessor,microcontroller, digital signal processor, field programmable gatearray, or application specific integrated circuit.

The transmitter 202 can be configured to modulate data or other contentfor transmission by at least one antenna 210. The transmitter 202 canalso be configured to amplify, filter and a frequency convert RF signalsbefore such signals are provided to the antenna 210 for transmission.The transmitter 202 can include any suitable structure for generatingsignals for wireless transmission.

The receiver 204 can be configured to demodulate data or other contentreceived by the at least one antenna 210. The receiver 204 can also beconfigured to amplify, filter and frequency convert RF signals receivedvia the antenna 210. The receiver 204 can include any suitable structurefor processing signals received wirelessly. The antenna 210 can includeany suitable structure for transmitting and/or receiving wirelesssignals. The same antenna 210 can be used for both transmitting andreceiving RF signals, or alternatively, different antennas 210 can beused for transmitting signals and receiving signals.

It is appreciated that one or multiple transmitters 202 could be used inthe UE 110, one or multiple receivers 204 could be used in the UE 110,and one or multiple antennas 210 could be used in the UE 110. Althoughshown as separate blocks or components, at least one transmitter 202 andat least one receiver 204 could be combined into a transceiver.Accordingly, rather than showing a separate block for the transmitter202 and a separate block for the receiver 204 in FIG. 2, a single blockfor a transceiver could have been shown.

The UE 110 further includes one or more input/output devices 212. Theinput/output devices 212 facilitate interaction with a user. Eachinput/output device 212 includes any suitable structure for providinginformation to or receiving information from a user, such as a speaker,microphone, keypad, keyboard, display, or touch screen.

In addition, the UE 110 includes at least one memory 206. The memory 206stores instructions and data used, generated, or collected by the UE110. For example, the memory 206 could store software or firmwareinstructions executed by the processor(s) 208 and data used to reduce oreliminate interference in incoming signals. Each memory 206 includes anysuitable volatile and/or non-volatile storage and retrieval device(s).Any suitable type of memory may be used, such as random access memory(RAM), read only memory (ROM), hard disk, optical disc, subscriberidentity module (SIM) card, memory stick, secure digital (SD) memorycard, and the like.

FIG. 3 illustrates an example BS 170 that may implement the methods andteachings according to this disclosure. As shown in the figure, the BS170 includes at least one processor 308, at least one transmitter 302,at least one receiver 304, one or more antennas 310, and at least onememory 306. The processor 308 implements various processing operationsof the BS 170, such as signal coding, data processing, power control,input/output processing, or any other functionality. Each processor 308includes any suitable processing or computing device configured toperform one or more operations. Each processor 308 could, for example,include a microprocessor, microcontroller, digital signal processor,field programmable gate array, or application specific integratedcircuit.

Each transmitter 302 includes any suitable structure for generatingsignals for wireless transmission to one or more UEs 110 or otherdevices. Each receiver 304 includes any suitable structure forprocessing signals received wirelessly from one or more UEs 110 or otherdevices. Although shown as separate blocks or components, at least onetransmitter 302 and at least one receiver 304 could be combined into atransceiver. Each antenna 310 includes any suitable structure fortransmitting and/or receiving wireless signals. While a common antenna310 is shown here as being coupled to both the transmitter 302 and thereceiver 304, one or more antennas 310 could be coupled to thetransmitter(s) 302, and one or more separate antennas 310 could becoupled to the receiver(s) 304. Each memory 306 includes any suitablevolatile and/or non-volatile storage and retrieval device(s).

The technology described herein can be implemented using hardware,software, or a combination of both hardware and software. The softwareused is stored on one or more of the processor readable storage devicesdescribed above to program one or more of the processors to perform thefunctions described herein. The processor readable storage devices caninclude computer readable media such as volatile and non-volatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer readablestorage media and communication media. Computer readable storage mediamay be implemented in any method or technology for storage ofinformation such as computer readable instructions, data structures,program modules or other data. Examples of computer readable storagemedia include RAM, ROM, EEPROM, flash memory or other memory technology,CD-ROM, digital versatile disks (DVD) or other optical disk storage,magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to storethe desired information and which can be accessed by a computer. Acomputer readable medium or media does (do) not include propagated,modulated or transitory signals.

Communication media typically embodies computer readable instructions,data structures, program modules or other data in a propagated,modulated or transitory data signal such as a carrier wave or othertransport mechanism and includes any information delivery media. Theterm “modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as RF and other wireless media.Combinations of any of the above are also included within the scope ofcomputer readable media.

In alternative embodiments, some or all of the software can be replacedby dedicated hardware logic components. For example, and withoutlimitation, illustrative types of hardware logic components that can beused include Field-programmable Gate Arrays (FPGAs),Application-specific Integrated Circuits (ASICs), Application-specificStandard Products (ASSPs), System-on-a-chip systems (SOCs), ComplexProgrammable Logic Devices (CPLDs), special purpose computers, etc. Inone embodiment, software (stored on a storage device) implementing oneor more embodiments is used to program one or more processors. The oneor more processors can be in communication with one or more computerreadable media/storage devices, peripherals and/or communicationinterfaces.

FIG. 4 illustrates exemplary details of a receiver 404, which can be thereceiver 204 included in the UE 110 (shown in FIG. 2) or the receiver304 included in the BS 170 (shown in FIG. 3), but is not limitedthereto. Referring to FIG. 4, the receiver 404 is shown as including aninput 406 at which is received a radio frequency (RF) signal, and thus,the input 406 can also be referred to as the RF input 406. The RF input406 can be coupled to an antenna or a coupler, but is not limitedthereto. The RF signal received by the RF input 406 is provided to a lownoise amplifier (LNA) 408, which may have an adjustable gain. The LNA408 amplifies the relatively low-power RF signal it receives withoutsignificantly degrading the signal's signal-to-noise ratio (SNR). Theamplified RF signal that is output by the LNA 408 is provided to a mixer410. The mixer 410, in addition to receiver the amplifier RF signal fromthe LNA 408, also receives an oscillator signal from a local oscillator,which in this case is a Phase Locked Loop (PLL) 431. Mixer 410 adjuststhe frequency of the amplifier RF signal, e.g., from a first frequencyto a second frequency that is lower than the first frequency. Morespecifically, the mixer 410 can be a down-mixer (DN MIX) that frequencydown-converts the amplified RF signal from a relatively high frequencyto a baseband frequency, or an intermediate frequency (IF) that isoffset from the baseband frequency. Thus, an oscillator signal from PLL431 is used as a carrier signal in receiver 404.

Still referring to FIG. 4, the frequency down-converted RF signal thatis output from the mixer 410 is shown as being provided to atrans-impedance amplifier (TIA) 412. The TIA 412 acts as a currentbuffer to isolate a multi-feedback (MFB) filter 414 that is downstreamof the TIA 412, from the mixer 410 that is upstream of the TIA 412. TheMBF filter 414 low pass filters the frequency down-converted RF signal,to filter out high frequency signal components that are not of interest,such as high frequency (HF) noise. The filtered RF signal that is outputfrom the MBF filter 414 is provided to a variable gain amplifier (VGA),which is used to amplify the RF signal before it provided to ananalog-to-digital converter (ND) 418, which converts the RF signal froman analog signal to a digital signal. The digital signal output from theND 418 is then provided to a digital filter 420, which performsadditional filtering to remove out of band signal components andattenuates quantization energy from the ND 418. The filtered digitalsignal that is output by the digital filter 420 is then provided tofurther digital circuitry that is downstream from the digital filter420. Such further digital circuitry can include, for example, a digitalsignal processor (DSP), but is not limited thereto. The same DSP, or adifferent DSP, can be used to implement the digital filter 420.

FIG. 5 illustrates exemplary details of a transmitter 502, which can bethe transmitter 202 included in the UE 110 (shown in FIG. 2) or thetransmitter 302 included in the BS 170 (shown in FIG. 3) but is notlimited thereto. Referring to FIG. 5, the transmitter 502 is shown asincluding a Digital-to-Analog Converter (D/A) 506, which converts adigital input (e.g. from processor 208 or processor 308) into an analogRF signal and provides the RF signal to a Low Pass Filter 508, whichfilters the RF signal and provides the filtered RF signal to mixer 510.Mixer 510, in addition to receiving the filtered RF signal from Low PassFilter 508, also receives a local oscillator signal from PLL 531 andadjusts the frequency of the RF signal, e.g. from a first frequency to asecond frequency that is higher than the first frequency. Morespecifically, mixer 510 may be an up-mixer (UP MIX) that frequencyup-converts the filtered RF signal from a relatively low frequency (e.g.baseband frequency, or an intermediate frequency (IF) that is offsetfrom the baseband frequency) to a relatively high frequency. Thus, anoscillator signal from PLL 531 is used as a carrier signal intransmitter 502. The RF signal from mixer 510 is then amplified by aPre-Power Amplifier (PPA) 512, and a Power Amplifier (PA) 514 andfiltered by a filter 516 before being provided to an RF output 518(RFout). For example, RF output 518 may be coupled to an antenna or acoupler but is not limited thereto.

FIG. 6 shows a schematic illustration of a PLL 631 (e.g. PLL 431 of FIG.4 or PLL 531 of FIG. 5), which may be used to provide a local oscillatorsignal for a transmitter (e.g. for transmitter 202 or transmitter 302)or for a receiver (e.g. for a receiver in user equipment or in a basestation, such as receiver 204 or receiver 304) or for any other purpose.PLL 531 may be incorporated into a common IC or a set of ICs with areceiver and/or transmitter (e.g. receiver 404 and/or transmitter 502)which may be packaged e.g. using flip-chip or metal bumping to formconnections to such ICs without using bond wires. A transmitter,receiver, or transceiver IC may include multiple PLLs to generateoscillator signals, which can be used as carrier signals, but are notlimited thereto.

PLL 631 includes a Phase Detector 640, which receives an input signal(e.g. a signal from a master oscillator) and a feedback signal via afeedback loop through a Frequency Divider 642 from the output of PLL 631(frequency divider 642 may be considered optional according to therelationship between an input frequency and output frequency). PhaseDetector 640 compares the input frequency and feedback frequency andgenerates an output according to the phase comparison, which is providedto Low Pass Filter 644. Low Pass Filter 644 removes high-frequency noiseto generate a Direct Current (DC) output according to the differencebetween the input frequency and the feedback frequency. The DC output isprovided to Voltage Controlled Oscillator, VCO 646, which adjusts thefrequency of its output signal according to the voltage it receives fromLow Pass Filter 644 in order to bring its output signal back to thefrequency of the input signal. Thus, the PLL provides an output with afrequency that locks onto the input frequency.

FIG. 7A shows an example of an implementation of a VCO 746 (e.g. VCO 646of FIG. 6 used in PLL 631) to provide a local oscillator signal for areceiver (such as receiver 404) or a transmitter (such as transmitter502). VCO 746 includes a resonant tank 748 and an amplifier 750 coupledto provide an electrical input to the resonant tank and amplify anelectrical signal in resonant tank 748. A control signal 752 (e.g. a DCvoltage from a phase detector and low pass filter in a PLL) is providedto resonant tank 748 to allow adjustment of a resonant frequency of thetank and thus the frequency of an output signal 754. Control signal 752may modify resonant frequency by changing characteristics of one or morecomponent of resonant tank 748. For example, in a resonant tank thatincludes a capacitor and an inductor (“an LC resonant tank”, or simply“an LC tank”), the capacitance of the capacitor may be modifiedaccording to a control signal (e.g. capacitor may be a variablecapacitor that has a variable capacitance, which can be varied accordingto the control signal).

In some cases, an LC tank may include an inductor which may be tapped sothat it has more than two terminals. For example, a tapped inductor mayinclude one or more tapped terminals at intermediate locations betweeninductor ends (i.e. between end terminals of an inductor). FIG. 7B showsan example of a VCO 760, in which LC tank 762 includes a capacitorcontrolled by control signal 768 and a tapped inductor that includes twotapped terminals in addition to two terminals at either end of theinductor. End terminals of an inductor of tapped LC tank 762 may beconnected to inputs of amplifier 764 while tapped terminals of theinductor of tapped LC tank 762 may be connected to outputs of amplifier764, one of which is provided as output signal 766. This may providecertain advantages. For example, an input signal from LC tank 762 toamplifier 764 may exceed the supply voltage restrictions of amplifier764. Since the input voltage is representative of the energy stored intapped LC tank 762, the VCO noise in VCO 760 may be lower for the sametotal inductance than a VCO using an untapped inductor (i.e. because theLC circuit voltage is higher). A tapped inductor may provide a betterSNR and higher Q value than a corresponding untapped inductor of thesame size. Since the input voltage to amplifier 764 may exceed the powersupply rails, the gain of amplifier 764 may be higher for a given powerconsumption. A detailed description of use of tapped inductors in a VCOis provided in U.S. Pat. No. 9,425,737, entitled “Tapped inductorvoltage controlled oscillator,” which is hereby incorporated byreference in its entirety.

Amplifiers such as amplifiers 750 and 764 that are used in a VCO may besingle ended amplifiers or differential amplifiers and both single endedand differential amplifiers may be used with tapped or untappedinductors. While a single ended amplifier has one input and one output,a differential amplifier has two inputs and two outputs. Both singleended and differential amplifiers may be inverting or non-inverting.

For example, FIG. 7C shows an example of a VCO 771 that includes asingle ended amplifier 770 connected to a resonant tank 772, whichincludes capacitor 774 and untapped inductor 776. FIG. 7C shows anexample of a VCO 780 that includes single ended amplifier 770 connectedto a resonant tank 782, which includes capacitor 774 and tapped inductor784. FIG. 7E shows an example of a VCO 786 that includes a differentialamplifier 788 connected to resonant tank 772, which includes capacitor774 and untapped inductor 776. FIG. 7F shows an example of a VCO 790that includes differential amplifier 788 connected to a resonant tank792, which includes capacitor 774 and tapped inductor 794, which in thisexample has two tapped terminals.

FIG. 8A illustrates an example of a simple schematic of an LC tank 848that may be used in a VCO, e.g. as resonant tank 748 of VCO 746. LC tank848 includes a capacitor 850 and an inductor 852 connected in parallel.Capacitor 850 may be a variable capacitor that is controlled by acontrol signal (not shown in FIG. 8A) to control the resonant frequencyof LC tank 848. Output terminals 854, 856 of LC tank 848 may beconnected to an amplifier (such as amplifier 750) and the voltage, V,across output terminals 854, 856 is shown in FIG. 8B. It can be seenthat the voltage is in the form of a sine wave in this example. Thefrequency of this signal, w, is the resonance frequency of LC tank 848and depends on inductance (L) and capacitance (C) according to thefollowing equation:

$\omega = \frac{1}{\sqrt{LC}}$

In general, the Signal to Noise Ratio (SNR) and Q factor of an outputsignal from an LC tank depends on the energy stored in the tank. Theenergy depends on the capacitance (C), inductance (L), voltage (V), andcurrent (I) according to the equation:

${E = {{\frac{1}{2}CV^{2}} = \frac{1}{2}}}{LI}^{2}$

To increase energy E and improve signal strength of a VCO at a fixedsupply voltage and fixed frequency, the capacitor may be made largerwhile the inductor may be made smaller to reduce impedance andfacilitate larger current. Similarly, to maintain the same energy andsignal strength as voltage is reduced, the inductor may be made smallerwhile the capacitor is made larger. Thus, the relative sizes of acapacitor and an inductor in an LC tank may change as voltage is reduced(e.g. to facilitate smaller devices with lower breakdown voltages).

FIG. 8C shows an example of a physical implementation of LC tank 848formed on a semiconductor substrate 860. Inductor 852 is formed as aloop of metal formed on semiconductor substrate 860, e.g. deposited in ablanket layer, patterned, and etched to form the loop shown. Capacitor850 may be formed of one or more capacitive elements that are formed bydepositing layers of conductive material separated by a dielectriclayer. While reducing inductor size and increasing capacitor size maywork for a range of voltages to give adequate SNR, there may be physicallimits on forming connections between components as component sizeschange. For example, it may be difficult to form a small enough loop ofmetal and to connect it to terminals of a large capacitor for highfrequencies (e.g. 12 GHz).

In general, an LC tank such as LC tank 848 stores energy and losesenergy. If energy is added faster than it is lost, the signal willincrease in power and amplitude. As the signal increases losses usuallyincrease as well, therefore a stable limit cycle occurs where the energyadded equals the energy lost. In some cases, an oscillator may startwith no external stimulation signal provided since an inductor alwayshas some resistance and the random motion of electrons in such aninductor provides Gaussian noise distributed across all frequencies. Asthe LC tank filters the noise, it shows a peak in the noise spectrum atthe resonant frequency. When an amplifier is attached to such an LC tank(e.g. as shown in the examples of FIGS. 7A-F) it amplifies that peaknoise and adds it to the energy of the resonant tank. This way anoscillator may start without any externally provided electricalstimulation, other than the noise present in the components of the LCtank themselves. Because the noise is of very low level it generallyrequires some time for an oscillator to reach its full amplitude.Therefore, in some cases, an electrical input, or external stimulationsignal, is applied to reduce the time required to reach full amplitude.Aspects of the present technology are applicable to implementations bothwith and without such stimulation signals.

FIG. 9A shows an alternative example of resonant tank in schematic form,LC tank 948, that may be used in a VCO, e.g. as resonant tank 748 of VCO746 of FIG. 7A. LC tank 948 includes two capacitors, capacitor 970 andcapacitor 972, and two inductors, inductor 974 and inductor 976, in aring configuration with each capacitor connected between a pair of theinductors (i.e. capacitor 970 is connected between inductor 974 andinductor 976, and so is capacitor 972), and with each inductor connectedbetween a pair of the capacitors (i.e. inductor 974 is connected betweencapacitor 970 and capacitor 972, and so is inductor 976). LC tank 948may be considered an example of a multi-element LC tank, ormulti-element resonator.

LC tank 948 provides certain advantages over LC tank 848. For example,for the same voltages across components in LC tank 848 and LC tank 948,and the same sized components, LC tank 948 may store more energy andthus provide a higher SNR. The resonant frequency, w, of LC tank 948depends on the inductance (L) of individual inductors 974, 976 and thecapacitance (C) of individual capacitors 970, 972 according to thefollowing equation:

$\omega = {\frac{1}{\sqrt{\left( {2L} \right)\left( \frac{C}{2} \right)}} = \frac{1}{\sqrt{LC}}}$

Thus, resonant frequency is the same as for LC tank 848 when componentsof equal size are used. The energy stored in LC tank 948 is twice theenergy E stored in LC tank 848 (i.e. each capacitor and inductor storesthe same as in LC tank 848, and there are twice as many capacitors andinductors). This energy, 2E, depends on the capacitance (C), inductance(L), voltage (V), and current (I) according to the equation:

${2E} = {{\frac{1}{2}\left( \frac{C}{2} \right)\left( {2V} \right)^{2}} = {\frac{1}{2}\left( {2L} \right)I^{2}}}$

Thus, for the same voltage, twice as much energy is stored and SNR maybe improved compared with LC tank 848. Or, energy and SNR may be kept atthe same levels as for LC tank 848 while using a lower voltage (e.g.half the voltage to maintain same energy and SNR). Some combination ofincreased SNR and reduced voltage may be used to obtain multiplebenefits.

FIGS. 9B and 9C show voltages at different locations of LC tank 948 ofFIG. 9A. FIG. 9B shows voltage V1 between terminal 980 and terminal 982as a function of time, while FIG. 9C shows voltage V2 between terminal984 and terminal 986 as a function of time. FIGS. 9B and 9C show similarperiodic signals that are out of phase (180 degrees out of phase in thisexample). Voltage V1 and/or V2 may be used to provide an output signalof LC tank 948 (and an output signal of a VCO that includes LC tank948). In order to allow tuning of LC tank 948, capacitor 970 and/orcapacitor 972 may be variable (i.e. may configured to have differentcapacitances) so that the output of LC tank 948 can be modified (e.g.according to a reference signal in a PLL).

FIG. 9D illustrates an example of a physical implementation of LC tank948 of FIG. 9A formed on a semiconductor substrate 960. Inductor 974 isformed as a portion of metal on semiconductor substrate 960, e.g.deposited in a blanket layer, patterned, and etched to form the partialloop shown. Inductor 976 is similarly formed as a portion of metal onsemiconductor substrate 960. In an example, inductors in an LC tank maybe formed of portions of metal that are half-loops (e.g. inductor 974may form half of a loop and inductor 976 may form the other half of theloop with breaks in the loop for capacitors). Capacitors 970, 972 may beformed of one or more capacitive elements that are formed by depositinglayers of conductive material separated by a dielectric layer.

Amplification of a signal in an LC tank may be provided by one or moreamplifiers connected to components of the LC tank in order to add energyand thus overcome energy loss from lossy elements of the LC tank. For anLC tank with a single capacitor in parallel with a single inductor,amplification may be provided across the capacitor and inductor. In anLC tank with two or more capacitors and two or more inductors such as LCtank 948 amplification can be provided at different locations and indifferent configurations as appropriate.

FIG. 10A shows an example of a VCO 1000 including LC tank 948 of FIG. 9Awith amplifier 1002 coupled to provide amplification across inductor 976and amplifier 1004 coupled to provide amplification across inductor 974.Amplifiers 1002, 1004 may be formed of any suitable circuits configuredto amplify a signal in LC tank 948. Amplifiers 1002 and 1004 may beconsidered collectively as an example implementation of amplifier 750 ofVCO 746 and may provide electrical input to LC tank 948 and amplify anelectrical signal to generate an oscillator signal at the resonantfrequency of LC tank 948.

FIG. 10B shows an example of an amplifier 1006 that may be used with anLC tank such as LC tank 948 of FIG. 10A (i.e. amplifier 1006 may be usedas amplifier 1002 and/or amplifier 1004). Amplifier 1006 is formed of adifferential inverter pair consisting of inverter 1008 and inverter1010, that are oppositely oriented. In this configuration, amplifier1006 can provide amplification in both directions, in both phases of asignal in LC tank 948.

FIG. 10C shows another example of an amplifier 1012 that may be usedwith an LC tank such as LC tank 948 of FIG. 10A (i.e. amplifier 1012 maybe used as amplifier 1002 and/or amplifier 1004). Amplifier 1012 isformed of an inverter 1014. In this configuration, amplifier 1012provides amplification in only one direction, in one phase of a signalin LC tank 948.

Capacitors in an LC tank may be variable capacitors that are formed oftwo or more capacitive elements that are configurable to varycapacitance. In an LC tank with more than one capacitor, one or morecapacitors may be variable capacitors to allow tuning of the resonantfrequency of the LC tank.

FIG. 10D shows a schematic illustration of a variable capacitor,capacitor 1020, that may be used in an LC tank such as LC tank 948 ofFIG. 10A (e.g. capacitor 1020 may be used as capacitor 970 and/orcapacitor 972). Capacitor 1020 includes a first capacitive element 1022and a second capacitive element 1024 with a switch 1026 to modifycapacitance of capacitor 1020 by a discrete amount according toconnection of first capacitive element 1022 and the second capacitiveelement 1024. Specifically, the first capacitive element 1022 and secondcapacitive element 1024 may be inactive (providing no contribution tocapacitance of capacitor 1020) when switch 1026 is open or may be active(contributing to capacitance of capacitor 1020) when switch 1026 isclosed. FIG. 10D also shows variable capacitive element 1028 andvariable capacitive element 1030 each with a respective capacitance thatis variable over a continuous range according to an applied voltage. Forexample, variable capacitive elements 1028, 1030 may be varactors withcapacitance varying according to applied voltage. While two variablecapacitive elements 1028, 1030 are shown in capacitor 1020, any numberof variable capacitive elements may be provided. And while a singleswitch is shown controlling coupling of capacitive element 1022 andcapacitive element 1024, it will be understood that a variable capacitormay include any number of capacitive elements in any suitableconfiguration (e.g. an array or bank of capacitive elements andswitches). A variable capacitor may include capacitive elements that areconfigurable by switches (e.g. capacitive elements 1022 and 1024, whichare configurable by switch 1026) and/or variable capacitive elementsthat are configurable to allow their capacitance to be modified (e.g.variable capacitive elements 1028, 1030). Switch 1026 and variablecapacitive elements may be controlled to change capacitance of capacitor1020 by discrete amounts and/or over a continuous range. A switch suchas switch 1026 may be formed of any suitable component or components.For example, one or more transistor may be used as a switch that isconfigurable to connect or disconnect components. Any suitablecomponents which can connect and disconnect circuit nodes may be used asswitches. In this way, course and fine adjustment of capacitance allowsprecise adjustment of resonant frequency, e.g. in response to a voltagefrom a phase detector in a PLL.

In an LC tank with two or more capacitors (e.g. capacitors 970 and 972of LC tank 948) one or more capacitor may be a variable capacitor. In asymmetric implementation of LC tank 948, capacitor 970 and capacitor 972are variable capacitors, e.g. as illustrated in FIG. 10D. Amplificationmay be symmetric in such an implementation so that both amplifier 1002and amplifier 1004 may be formed by pairs of inverters as illustrated inFIG. 10B. Output voltages V1 and V2 in this configuration may besymmetric with a phase difference of 180 degrees.

While FIG. 10A shows an example in which amplifiers 1002 and 1004 areconnected across inductors 976 and 974 respectively, other amplifier toinductor configurations are possible. For example, some inductors may betapped inductors with one or more tapped terminals (in addition toterminals at either end). Tapped inductors may have connections to theirtapped terminals in addition to their end terminals at inductor ends.

FIG. 11A shows an example of an inductor 1101 that is a tapped inductor.In addition to end terminals 1102 and 1104, inductor 1101 includes atapped terminal 1106 that connects to an intermediate location betweenend terminal 1102 and end terminal 1104. Thus, in addition to metal loop1108, which extends between end terminal 1102 and end terminal 1104,inductor 1101 includes metal connector 1110, which connects from anintermediate location of metal loop 1108 to tapped terminal 1106, thusallowing coupling of an input or output at an intermediate location. Forexample, in some cases, it may be advantageous to couple an amplifierbetween an end terminal and a tapped input terminal (e.g. between endterminal 1102 and tapped terminal 1106) and thus provide an inputthrough a tapped terminal. End terminals may be connected to othercomponents, e.g. connecting to capacitors in a ring arrangement such asin LC tank 948.

FIG. 11B shows an example of a schematic illustration of animplementation of a VCO 1100 including LC tank 948 of FIG. 9A usingtapped inductors such as inductor 1101 of FIG. 11A, i.e. where inductors974 and 976 of LC tank 948 are tapped inductors. Amplification isprovided to inductors 974, 976 through tapped input terminals.Specifically, amplifier 1002 is connected to tapped terminal 1112 ofinductor 976 and amplifier 1004 is connected to tapped terminal 1114 ofinductor 974. Amplifiers 1002 and 1004 may be considered collectively asan example implementation of amplifier 764 of VCO 760 and may provideelectrical input to LC tank 948 and amplify an electrical signal in LCtank 948 to generate an oscillator signal at the resonant frequency ofLC tank 948 (e.g. voltage V1 or V2 may be an oscillator signal).

FIG. 11C shows a more detailed example of VCO 1100 (which may beconsidered an example of how VCO 1100 may be implemented usingparticular components including tapped inductors, inverters connected totapped terminals of the tapped inductors, and variable capacitors).Amplifier 1002 is implemented by a single inverter 1152 that has itsoutput connected to tapped terminal 1112 of inductor 976. Amplifier 1004is implemented by a single inverter 1154 that has its output connectedto tapped terminal 1114 of inductor 974. Thus, amplification in VCO 1100is provided by a pair of differential inverters including inverter 1152and inverter 1154. Capacitor 970 and capacitor 972 are implemented asvariable capacitors, each with a capacitance that is variable over arange to control a resonant frequency of LC tank 948. Capacitor 972includes capacitive element 1158 and capacitive element 1160 with switch1162 to modify a capacitance of capacitor 972 by discrete amountsaccording to connection of capacitive element 1158 and capacitiveelement 1160. Capacitor 972 includes variable capacitive elements 1164and 1166 each with a respective capacitance that is variable over acontinuous range according to an applied voltage. Capacitor 970 mayinclude similar components to those shown in Capacitor 972 so that thecapacitance of capacitor 970 may also be configured (components ofcapacitor 970 are omitted from FIG. 11C). It can be seen that VCO 1100provides a simpler implementation than a symmetric implementation.

While LC tank 948 of the above examples is illustrated as including twocapacitors and two inductors in a ring configuration, in alternatingorder (capacitor, inductor, capacitor, inductor), the present technologyis not limited to any particular number of components and may beimplemented with more than two inductors and more than two capacitors,e.g. three capacitors and three inductors, four capacitors and fourinductors, five capacitors and five inductors, etc.

FIG. 12 shows an example of an LC tank 1200 that includes fourcapacitors 1202, 1204, 1206, and 1208 and four inductors 1212, 1214,1216, and 1218 connected in a ring configuration with each capacitorconnected in series between a pair of the inductors and each inductorconnected in series between a pair of the capacitors. For example,capacitor 1202 is connected between inductors 1218 and 1212, capacitor1204 is connected between inductors 1212 and 1214, and so on, andinductor 1212 is connected between capacitors 1202 and 1204, inductor1214 is connected between capacitors 1204 and 1206 and so on. Such aring configuration may be extended to any number of components and isnot limited to two-capacitor, two-inductor examples (e.g. LC tank 948)and four-capacitor, four-inductor examples (e.g. LC tank 1200) that areshown in the drawings. It will be understood that the term “ringconfiguration” may refer to two-terminal elements such as capacitors andinductors that are connected in series, or concatenated, such that oneand only one terminal of any element is connected to one and only oneterminal of the next element in a closed loop (tapped terminals are notused for connection to capacitors so that inductors may be consideredtwo-terminal elements for purposes of forming such connections). One ormore of capacitors 1202, 1204, 1206, and 1208 may be variable capacitorsto tune the resonant frequency of LC tank 1200. One or more of inductors1212, 1214, 1216, and 1218 may be tapped inductors to allow connectionof amplifiers to tapped terminals.

Circuits described above may be used in various applications. Methods ofusing a resonant tank, such as LC tank 948 or LC tank 1200, aresummarized with reference to the high level flow diagram shown in FIG.13. Referring to FIG. 13, step 1300 involves providing an electricalinput to a resonant tank that includes a first capacitor, a firstinductor, a second capacitor, and a second inductor, formed on thesemiconductor substrate, and connected in a ring configuration with eachcapacitor connected in series between inductors, and with each inductorconnected in series between capacitors. For example, one or moreamplifiers may be connected to terminals of a resonant tank to providean electrical input to the resonant tank. Still referring to FIG. 13,step 1302 involves amplifying an electrical signal generated from theelectrical input in the resonant tank to generate the oscillator signalat a resonant frequency of the resonant tank. For example, a resonanttank may generate an electrical signal at a resonant frequency and anamplifier may amplify this electrical signal to generate the oscillatorsignal (e.g. oscillator signal of a VCO).

It is understood that the present subject matter may be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this subject matter will be thorough and complete and will fullyconvey the disclosure to those skilled in the art. Indeed, the subjectmatter is intended to cover alternatives, modifications and equivalentsof these embodiments, which are included within the scope and spirit ofthe subject matter as defined by the appended claims. Furthermore, inthe following detailed description of the present subject matter,numerous specific details are set forth in order to provide a thoroughunderstanding of the present subject matter. However, it will be clearto those of ordinary skill in the art that the present subject mattermay be practiced without such specific details.

The description of the present disclosure has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of thedisclosure. The aspects of the disclosure herein were chosen anddescribed in order to best explain the principles of the disclosure andthe practical application, and to enable others of ordinary skill in theart to understand the disclosure with various modifications as aresuited to the particular use contemplated.

Although the present disclosure has been described with reference tospecific features and embodiments thereof, it is evident that variousmodifications and combinations can be made thereto without departingfrom scope of the disclosure. The specification and drawings are,accordingly, to be regarded simply as an illustration of the disclosureas defined by the appended claims, and are contemplated to cover any andall modifications, variations, combinations or equivalents that fallwithin the scope of the present disclosure. Although the subject matterhas been described in language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed as example forms of implementingthe claims.

The invention claimed is:
 1. An apparatus, comprising: A first inductor having a first end and a second end, a second inductor having a first end and a second end, a first capacitor having a first end and a second end, a second capacitor having a first end and a second end; a first amplifier having a first end and a second end; a second amplifier having a first end and a second end; wherein: the first end of the first capacitor is coupled to the first end of the first inductor, and the second end of the first capacitor is coupled to the first end of the second inductor; the first end of second capacitor is coupled to the second end of the first inductor, and the second end of the second capacitor is coupled to the second end of the second inductor; the first amplifier is coupled to provide an amplification across the first inductor; and the second amplifier is coupled to provide an amplification across the second inductor; and wherein the first inductor further having a first tapped end, wherein the first end of the first amplifier is coupled to the first end of the first inductor, and the second end of the first amplifier is coupled to the first tapped end of the first inductor.
 2. The apparatus of claim 1, wherein the first amplifier is coupled to provide amplification of signal with opposite directions.
 3. The apparatus of claim 1, wherein the first end of the first amplifier is coupled to the first end of the first inductor, and the second end of the first amplifier is coupled to the second end of the first inductor; wherein the first end of the second amplifier is coupled to the first end of the second inductor, and the second end of the second amplifier is coupled to the second end of the second inductor.
 4. The apparatus of claim 1, wherein the first amplifier comprises a first inverter, wherein the input of the first inverter is coupled to the first end of the amplifier, and the output of the first inverter is coupled to the second end of the first amplifier.
 5. The apparatus of claim 4, wherein the first amplifier further comprises a second inverter, wherein the second inverter and the first inverter are coupled with opposite orientation.
 6. The apparatus of claim 1, wherein the second inductor further having a first tapped end, wherein the first end of the second amplifier is coupled to the first end of the second inductor, and the second end of the first amplifier is coupled to first tapped end of the first inductor.
 7. The apparatus of claim 1, wherein the first capacitor comprise a first tunable capacitor and a second tunable capacitor coupled in series.
 8. The apparatus of claim 7, wherein the first capacitor comprise a first fixed capacitor and a second fixed capacitor coupled in series through a switch.
 9. The apparatus of claim 1, wherein the apparatus forms a Voltage Controlled Oscillator (VCO) in a Phase Locked Loop (PLL) circuit that further includes a feedback loop, a phase detector, and a filter.
 10. An oscillator circuit, comprising: a first inductor having a first end and a second end, a second inductor having a first end and a second end; a first amplifier having a first end and a second end, a second amplifier having a first end and a second end; wherein the first end of the first amplifier comprises two differential inputs, the second end of the first amplifier comprises two differential outputs; wherein the first inductor comprises two tapped ends; wherein the two differential outputs of the first amplifier are coupled to the two tapped ends of the first inductor, and the two differential inputs of the first amplifier are respectively coupled to the first end and the second end of the first inductor.
 11. The oscillator circuit of claim 10, wherein the first end of the second amplifier comprises two differential inputs, the second end of the second amplifier comprises two differential outputs; wherein the second inductor comprises two tapped ends; wherein the two differential outputs of the second amplifier are coupled to the two tapped ends of the second inductor, and the two differential inputs of the second amplifier are respectively coupled to the first end and the second end of the second inductor.
 12. The oscillator circuit of claim 11, further comprising a first capacitor having a first end and a second end, a second capacitor having a first end and a second end; wherein the first end of the first capacitor is coupled to the first end of the first inductor, and the second end of the first capacitor is coupled to the first end of the second inductor; the first end of second capacitor is coupled to the second end of the first inductor, and the second end of the second capacitor is coupled to the second end of the second inductor.
 13. The oscillator circuit of claim 12, wherein the first capacitor comprise a first tunable capacitor and a second tunable capacitor coupled in series.
 14. The oscillator circuit of claim 13, wherein the first capacitor comprise a first fixed capacitor and a second fixed capacitor coupled in series through a switch.
 15. An oscillator circuit, comprising: A first inductor having a first end and a second end, a second inductor having a first end and a second end, a first capacitor having a first end and a second end, a second capacitor having a first end and a second end; a first amplifier having a first end and a second end; a second amplifier having a first end and a second end; wherein: the first end of the first capacitor is coupled to the first end of the first inductor, and the second end of the first capacitor is coupled to the first end of the second inductor; the first end of second capacitor is coupled to the second end of the first inductor, and the second end of the second capacitor is coupled to the second end of the second inductor; the first amplifier is coupled to provide an amplification across the first inductor; and the second amplifier is coupled to provide an amplification across the second inductor; wherein the first capacitor comprise a first tunable capacitor and a second tunable capacitor coupled in series.
 16. An oscillator circuit of claim 15, wherein the first capacitor comprise a first fixed capacitor and a second fixed capacitor coupled in series through a switch. 